(a) Technical Field of the Invention
The present invention relates to a method of preparation of α,α,α′,α′-tetrafluoro-p-xylene, in particular, to a preparation method using α,α,α′,α′-tetrafluoro-p-xylene and KF with phase transfer catalyst.
(b) Description of the Prior Art
Russian Patent No. Ru 2032654 (1995) discloses the preparation of α,α,α′,α′-tetrafluoro-p-xylene by reacting α,α,α′,α′-tetrabromo-p-xylene and SbF3 at 100–150° C./20–100 mm Hg. The methods of preparation of α,α,α′,α′-tetrafluoro-p-xylene are as follows:

EP No. 949663 (1999) discloses the preparation of α,α,α′,α′-tetrafluoro-p-xylene by reacting terephthol aldehyde and 1,2-ethanedithiol, and then with HF/pyridine, under reduced pressure and distillation. The reaction is as follows:
α,α,α′,α′-tetrafluoro-p-xylene by reacting α,α,α′,α′-tetrachloro-p-xylene with HF at 70° C., 7 kg/cm2. The reaction is as follows:

EP Patent No. 970938 (2000) discloses the preparation of α,α,α′,α′-tetrafluoro-p-xylene by reacting para-phthalic aldehyde with SF4/HF. The reaction is as follows:

WO9824743 (1998) by Dolbier, William R., Jr., Rong, Xiao X., Stalzer, Walter E, discloses the preparation of α,α,α′,α′-tetrafluoro-p-xylene by stirring α,α,α′,α′-tetrachloro-p-xylene with alkali metal fluoride such as potassium fluoride at high temperature without solvent. The reaction is as follows:

In this method, the alkaline fluoride is cheap and stable. But it has a difficulty in stirring. When α,α,α′,α′-tetrachloro-p-xylene is 8 equivalent of KF, and without stirring, it takes 7 days to react under 240° C. In addition the yield is about 54%, and a partial of the fluoride will be decomposed and it forms a lump with the metallic salt, which is difficult to dissolve in water and organic solvent such as hexane, ether, ketone, methanol, ethanol, CH2Cl2, CH3Cl, CCl4, THF, dioxane, NMP, OMF, acetic acid, ethyl ester, benzene, phenyl, etc. Thus, it is difficult to clean the reactor.